Lamp failure detecting device, method for setting lamp failure detecting device, light source failure detecting device, method for setting light source failure detecting device, and lamp assembly

ABSTRACT

Each of a low beam lamp and a high beam lamp connected in series includes at least one light source. A lamp driving circuit is configured to supply current to each of the n lamps. A first voltage detecting circuit is configured to detect a first voltage that is a sum of voltages applied to each of the low beam lamp and the high beam lamp. A second voltage detecting circuit is configured to detect a second voltage that is applied to the high beam lamp. A processor is configured to obtain a difference between the first voltage and the second voltage, and to detect a failure in the low beam lamp based on comparison between the difference and a rewritable normal operation voltage of the low beam lamp.

TECHNICAL FIELD

The presently disclosed subject matter relates to a lamp failure detecting device adapted to be installed in a vehicle and a method of setting the lamp failure detecting device. The lamp failure detecting device detects at least one failure of a plurality of lamps installed in the vehicle and connected in series. The present disclosure also relates to a light source failure detecting device adapted to be installed in a vehicle, and a method of setting the light source failure detecting device. The light source failure detecting device detects at least one failure of a plurality of light sources installed in a vehicle and connected in series. The present disclosure also relates to a lamp assembly comprising the plurality of lamps and the lamp failure detecting device, or the plurality of light sources and the light source failure detecting device.

BACKGROUND

A lamp control device described in Japanese Patent Publication No. 2007-200610 A controls lighting operation of a plurality of lamps installed in a vehicle. The lamps are connected in series to a lamp control device. The lamp control device includes a plurality of forward voltage detecting circuits and a microcomputer. Each of the plurality of forward voltage detecting circuits detects a forward voltage applied to a corresponding one of the plurality of lamps. The microcomputer detects a short-circuit failure of each lamp based on a comparison result between the forward voltage detected by each forward voltage detecting circuit and a predetermined abnormality determination value.

SUMMARY

It is demanded to provide a more versatile technique for detecting failure in a plurality of lamps or a plurality of light sources installed in a vehicle and connected in series.

An illustrative aspect of the presently disclosed subject matter capable of meeting the above demand provides a lamp failure detecting device adapted to be installed in a vehicle, comprising:

-   -   a first voltage detecting circuit configured to detect a first         voltage that is a sum of voltages applied to, among n lamps (n         is an integer no less than 2) connected in series each of which         includes at least one light source, each of a first lamp to an         m-th lamp (m is an integer no less than 2 and no more than n)         from a grounding side;     -   a second voltage detecting circuit configured to detect a second         voltage that is a sum of voltages applied to each of the first         lamp to an (m−1)th lamp from the grounding side; and     -   a processor configured to obtain a difference between the first         voltage and the second voltage, and to detect a failure in the         m-th lamp based on comparison between the difference and a         rewritable threshold value.

An illustrative aspect of the presently disclosed subject matter capable of meeting the above demand provides a method of setting the above lamp failure detecting device, comprising:

-   -   selecting the m-th lamp to be connected to a lamp driving         circuit from which current is supplied;     -   obtaining a normal operation voltage of the m-th lamp that is to         be applied when the m-th lamp is operating normally; and     -   enabling the processor to reference the normal operation voltage         as the threshold value.

According to the above configuration, the voltage itself applied to the m-th lamp from the grounding side among the n lamps each including at least one light source and connected in series is not detected by a specific voltage detecting circuit. Instead, the difference between the first voltage, which is the sum of the voltages applied to each of the first lamp to the m-th lamp from the grounding side, and the second voltage, which is the sum of the voltages applied to each of the first lamp to the (m−1)th lamp from the grounding side, is treated as the voltage applied to the m-th lamp and is subjected to comparison with the threshold value that is to be referenced by the processor.

On the other hand, according to the setting method as described above, the threshold value to be referenced by the processor is rewritten in accordance with the normal operation voltage of the m-th lamp selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage of the m-th lamp is eliminated, and both the short-circuit failure and the open failure of the m-th lamp are accurately determined by the comparison between the difference value and the threshold value related to the normal operation voltage of the m-th lamp that is actually connected to the lamp driving circuit.

Further, since the threshold value to be referenced by the processor is rewritten according to the specification of the n lamps selected to be driven, the voltage detecting circuit can be shared by the n lamps having different specifications. Since the voltage detecting circuit has only to have at least the function of detecting the first voltage and the second voltage described above, the configuration can be simplified even though both the short-circuit failure and the open failure of each lamp can be determined.

Therefore, it is possible to improve the versatility of the lamp failure detecting device for detecting the failure of a plurality of lamps installed in the vehicle and connected in series.

Accordingly, an illustrative aspect of the presently disclosed subject matter capable of meeting the above demand provides a lamp assembly adapted to be installed in a vehicle, comprising:

-   -   n lamps (n is an integer no less than 2) connected in series,         each of which includes at least one light source;     -   a lamp driving circuit configured to supply current to each of         the n lamps;     -   a first voltage detecting circuit configured to detect a first         voltage that is a sum of voltages applied to each of a first         lamp to an m-th lamp (m is an integer no less than 2 and no more         than n) from a grounding side;     -   a second voltage detecting circuit configured to detect a second         voltage that is a sum of voltages applied to each of the first         lamp to an (m−1)th lamp from the grounding side; and     -   a processor configured to obtain a difference between the first         voltage and the second voltage, and to detect a failure in the         m-th lamp based on comparison between the difference and a         rewritable threshold value.

The above lamp assembly may be configured so as to comprise:

-   -   a switch configured to determine whether or not the current is         supplied to at least one of the first lamp to an (n−1)th lamp         from the grounding side.

According to such a configuration, the ON/OFF state of at least one of the plurality of lamps connected in series to the lamp driving circuit can be individually controlled.

The above lamp assembly may be configured such that:

-   -   the n-th lamp from the grounding side is a low beam lamp; and     -   at least one lamp except the n-th lamp is a high beam lamp.

An illustrative aspect of the presently disclosed subject matter capable of meeting the above demand provides a light source failure detecting device adapted to be installed in a vehicle, comprising:

-   -   a first voltage detecting circuit configured to detect a first         voltage that is a sum of voltages applied to, among n light         sources (n is an integer no less than 2) connected in series,         each of a first light source to an m-th light source (m is an         integer no less than 2 and no more than n) from a grounding         side;     -   a second voltage detecting circuit configured to detect a second         voltage that is a sum of voltages applied to each of the first         light source to an (m−1)th light source from the grounding side;         and     -   a processor configured to obtain a difference between the first         voltage and the second voltage, and to detect a failure in the         m-th light source based on comparison between the difference and         a rewritable threshold value.

An illustrative aspect of the presently disclosed subject matter capable of meeting the above demand provides a method of setting the above light source failure detecting device, comprising:

-   -   selecting the m-th light source to be connected to a light         source from which current is supplied;     -   obtaining a normal operation voltage of the m-th light source         that is to be applied when the m-th light source is operating         normally; and     -   enabling the processor to reference the normal operation voltage         as the threshold value.

According to the above configuration, the voltage itself applied to the m-th light source from the grounding side among the n light sources each including at least one light source and connected in series is not detected by a specific voltage detecting circuit. Instead, the difference between the first voltage, which is the sum of the voltages applied to each of the first light source to the m-th light source from the grounding side, and the second voltage, which is the sum of the voltages applied to each of the first light source to the (m−1)th light source from the grounding side, is treated as the voltage applied to the m-th light source and is subjected to comparison with the threshold value that is to be referenced by the processor.

On the other hand, according to the setting method as described above; the threshold value to be referenced by the processor is rewritten in accordance with the normal operation voltage of the m-th light source selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage of the m-th light source is eliminated, and both the short-circuit failure and the open failure of the m-th light source are accurately determined by the comparison between the difference value and the threshold value related to the normal operation voltage of the m-th light source that is actually connected to the light source driving circuit.

Further, since the threshold value to be referenced by the processor is rewritten according to the specification of the n light sources selected to be driven, the voltage detecting circuit can be shared with the n light sources having different specifications. Since the voltage detecting circuit has only to have at least the function of detecting the first voltage and the second voltage described above, the configuration can be simplified even though both the short-circuit failure and the open failure of each light source can be determined.

Therefore, it is possible to improve the versatility of the lamp failure detecting device for detecting the failure of a plurality of light sources installed in the vehicle and connected in series.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of a lamp assembly according to one embodiment.

FIG. 2 illustrates a configuration of a lamp failure detecting device according to one embodiment.

FIG. 3 illustrates another configuration of the lamp failure detecting device illustrated in FIG. 2.

FIG. 4 illustrates a configuration of a lamp failure detecting device according to another embodiment.

FIG. 5 illustrates a configuration of a light source failure detecting device according to one embodiment.

DESCRIPTION OF EMBODIMENTS

Examples of embodiments will be described below in detail with reference to the accompanying drawings. In each of the drawings used in the following description, the scale is appropriately changed in order to make each of the members have a recognizable size.

FIG. 1 illustrates a configuration of a lighting device 100 adapted to be installed in a vehicle. The lighting device 100 includes a housing 101 and a translucent cover 102. The housing 101 and the translucent cover 102 define a lamp chamber 103. The lamp assembly 1 according to one embodiment is accommodated in the lamp chamber 103.

The lamp assembly 1 includes a low beam lamp 11 and a high beam lamp 12. The low beam lamp 11 illuminates a region including a road surface located at a relatively short distance ahead of the vehicle. The high beam lamp 12 is a lamp that supplies illumination light to a relatively long distance ahead of the vehicle. The translucent cover 102 illustrated in FIG. 1 allows passage of light emitted from each of the low beam lamp 11 and the high beam lamp 12.

The lamp assembly 1 includes a lamp control device 13. The low beam lamp 11 and the high beam lamp 12 are electrically connected to the lamp control device 13. The lamp control device 13 is a device configured to control the turning-on/off operations of each of the low beam lamp 11 and the high beam lamp 12.

FIG. 2 schematically illustrates a configuration of the lamp assembly 1 according to one embodiment. The low beam lamp 11 and the high beam lamp 12 are electrically connected in series.

Each of the low beam lamp 11 and the high beam lamp 12 includes at least one light source. The light source may be a semiconductor light emitting element such as a light emitting diode (LED) or a laser diode (LD), or may be a lamp light source such as a halogen lamp or an HID lamp. When at least one of the low beam lamp 11 and the high beam lamp 12 includes a plurality of light sources, the plurality of light sources are electrically connected in series.

The high beam lamp 12 is an example of the first lamp from the grounding side. The low beam lamp 11 is an example of an m-th lamp (m=2) from the grounding side.

The lamp control device 13 includes a lamp driving circuit 131. The lamp driving circuit 131 is a circuit configured to supply current for lighting the low beam lamp 11 and the high beam lamp 12. The lamp driving circuit 131 may be implemented by, for example, a step-down constant-current switching regulator (DC/DC converter).

The lamp control device 13 includes a switch 132. The switch 132 may be implemented as a semiconductor switch, such as a field effect transistor. The switch 132 is a circuit configured to form a path for bypassing the current supplied from the lamp driving circuit 131 to the high beam lamp 12.

The lamp control device 13 includes a processor 133. The processor 133 is configured to control the operation of the switch 132 to control the turning on/off operations of the low beam lamp 11 and the high beam lamp 12. The processor 133 is configured to output a control signal SC for switching the open/close states of the switch 132. The control signal SC may be, for example, a signal for changing a control terminal voltage of a corresponding semiconductor switch.

When the switch 132 is closed by the control signal SC, a path through which current is supplied from the lamp driving circuit 131 to the low beam lamp 11 only while bypassing the high beam lamp 12 is formed. As a result, only the low beam lamp 11 is turned on.

When the switch 132 is opened by the control signal SC, a path is so formed that current is supplied from the lamp driving circuit 131 to both the low beam lamp 11 and the high beam lamp 12. As a result, the low beam lamp 11 and the high beam lamp 12 are turned on.

The lamp assembly 1 includes a first voltage detecting circuit 141. The first voltage detecting circuit 141 is configured to detect a first voltage V1 which is a sum total of a voltage VL applied to the low beam lamp 11 and a voltage VH applied to the high beam lamp 12. A first voltage signal SV1 corresponding to the first voltage V1 is inputted to the processor 133.

The first voltage detecting circuit 141 can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 2. Resistance values of respective resistive elements constituting the voltage dividing circuit can be appropriately determined based on a rated voltage applied to the low beam lamp 11 and the high beam lamp 12 and the voltage of the first voltage signal SV1 that can be inputted to the processor 133. Depending on the specification of the processor 133, the first voltage detecting circuit 141 may include an A/D conversion circuit.

The lamp assembly 1 includes a second voltage detecting circuit 142. The second voltage detecting circuit 142 is configured to detect the second voltage V2 corresponding to the voltage VH applied to the high beam lamp 12. The second voltage signal SV2 corresponding to the second voltage V2 is inputted to the processor 133.

The second voltage detecting circuit 142 can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 2. Resistance values of respective resistive elements constituting the voltage dividing circuit may be appropriately determined based on a rated voltage applied to the high beam lamp 12 and the voltage of the second voltage signal SV2 that can be inputted to the processor 133. Depending on the specification of the processor 133, the second voltage detecting circuit 142 may include an A/D conversion circuit.

The lamp assembly 1 includes a storage 134. The storage 134 can be implemented by an appropriate rewritable semiconductor memory. The storage 134 stores data NDL indicating a normal operation voltage NVL that is to be applied when the low beam lamp 11 is operating normally, and data NDH indicating a normal operation voltage NVH that is to be applied when the high beam lamp 12 is operating normally. The data NDL and the data NDH are configured to be rewritable. The normal operation voltage NVL may be defined as a voltage range having an upper limit value and a lower limit value. The normal operation voltage NVH may be defined as a voltage range having an upper limit value and a lower limit value.

The processor 133 is configured to detect failure of each of the low beam lamp 11 and the high beam lamp 12 based on the first voltage signal SV1 and the second voltage signal SV2.

First, the processor 133 obtains a difference VD between the first voltage V1 and the second voltage V2 based on the first voltage signal SV1 and the second voltage signal SV2. The difference value VD corresponds to the voltage VL applied to the low beam lamp 11.

Subsequently, the processor 133 compares the difference value VD with the normal operation voltage NVL indicated by the data NDL stored in the storage 134. If the difference value VD (i.e., the voltage VL) is equal to the normal operation voltage NVL, the processor 133 determines that the low beam lamp 11 is operating normally. The normal operation voltage NVL is an example of the threshold value.

If the difference value VD (i.e., the voltage VL) is more than the normal operation voltage NVL, the processor 133 determines that an open failure has occurred in the low beam lamp 11. If the difference value VD (i.e., the voltage VL) is less than the normal operation voltage NVL, the processor 133 determines that a short-circuit failure has occurred in the low beam lamp 11. An extent of which the difference value VD is more than the normal operation voltage NVL can be determined as appropriate to determine whether the open failure has occurred. An extent of which the difference value VD is less than the normal operation voltage NVL to determine that the short-circuit failure has occurred can be appropriately determined.

If any failure is detected in the low beam lamp 11, the processor 133 outputs a detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify an occupant of the vehicle that a failure has occurred in the low beam lamp 11, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

Similarly, the processor 133 compares the second voltage V2 corresponding to the second voltage signal SV2 with the normal operation voltage NVH indicated by the data NDH stored in the storage 134. If the second voltage V2 (i.e., the voltage VH) is equal to the normal operation voltage NVH, the processor 133 determines that the high beam lamp 12 is operating normally.

If the second voltage V2 (i.e., the voltage VH) is more than the normal operation voltage NVH, the processor 133 determines that an open failure has occurred in the high beam lamp 12. If the second voltage V2 (i.e., the voltage VH) is less than the normal operation voltage NVH, the processor 133 determines that a short-circuit failure has occurred in the high beam lamp 12. An extent of which the second voltage V2 is more than the normal operation voltage NVH to determine whether the open failure has occurred can be appropriately determined. An extent of which the second voltage V2 is less than the normal operation voltage NVH to determine whether the short-circuit failure has occurred can be appropriately determined.

If any failure is detected in the high beam lamp 12, the processor 133 outputs a detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify an occupant of the vehicle that a failure has occurred in the high beam lamp 12, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

The first voltage detecting circuit 141, the second voltage detecting circuit 142, and the processor 133 constitute a lamp failure detecting device 15.

As described above, the data NDL and the data NDH stored in the storage 134 are rewritable. Therefore, the lamp failure detecting device 15 can be initialized by the following procedure.

First, a low beam lamp 11 and a high beam lamp 12 constituting the lamp assembly 1 are selected. The selected low beam lamp 11 and high beam lamp 12 are electrically connected in series to a lamp control device 13.

The normal operation voltage NVL applied to the low beam lamp 11 when it is operating normally differs from individual to individual. Thus, the normal operation voltage NVL of the selected low beam lamp 11 is obtained through measurement.

Similarly, in the high beam lamp 12, the normal operation voltage NVH applied when the lamp 12 is operating normally differs from individual to individual. Thus, the normal operation voltage NVH of the selected high beam lamp 12 is obtained through measurement.

Subsequently, the data NDL corresponding to the acquired normal operation voltage NVL of the low beam lamp 11 is stored in the storage 134. In other words, the processor 133 is placed in a condition that is able to reference the normal operation voltage NVL. When any data NDL has already stored in the storage 134, it is rewritten with the data NDL corresponding to the newly acquired normal operation voltage NVL.

Similarly, data NDH corresponding to the acquired normal operation voltage NVH of the high beam lamp 12 is stored in the storage 134. In other words, the processor 133 is placed in a condition that is able to reference the normal operation voltage NVH. When any data NDH has already stored in the storage 134, it is rewritten with the data NDH corresponding to the newly acquired normal operation voltage NVH.

According to the above configuration, the voltage VL itself applied to the low beam lamp 11 is not detected by a specific voltage detecting circuit. Instead, the difference value VD between the first voltage V1, which is the sum of the voltages applied to the low beam lamp 11 and the high beam lamp 12, and the second voltage V2, which corresponds to the voltage VH applied to the high beam lamp 12, is treated as the voltage VL applied to the low beam lamp 11 and is subjected to comparison with the normal operation voltage NVL that is to be referenced by the processor 133.

On the other hand, the data NDL indicating the normal operation voltage NVL and to be referenced by the processor 133 is rewritten in accordance with the specification of the low beam lamp 11 selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage NVL of the low beam lamp 11 is eliminated, and both the short-circuit failure and the open failure of the low beam lamp 11 are accurately determined by the comparison between the difference value VD and the normal operation voltage NVL of the low beam lamp 11 that is actually connected to the lamp driving circuit 131.

In addition, since the data NDL indicating the normal operation voltage NVL and to be referenced by the processor 133 is rewritten according to the specification of the low beam lamp 11 selected to be driven, the first voltage detecting circuit 141 and the second voltage detecting circuit 142 can be shared by a plurality of low beam lamps 11 having different specifications. Since each of the first voltage detecting circuit 141 and the second voltage detecting circuit 142 has only to have at least the function of detecting the first voltage V1 and the second voltage V2 described above, the configuration can be simplified even though both the short-circuit failure and the open failure of the low beam lamp 11 can be determined.

Similarly, the data NDH indicating the normal operation voltage NVH and to be referenced by the processor 133 is rewritten in accordance with the specification of the high beam lamp 12 selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage NVH of the high beam lamp 12 is eliminated, and both the short-circuit failure and the open failure of the high beam lamp 12 are accurately determined by the comparison between the normal operation voltage NVH and the second voltage V2 of the high beam lamp 12 that is actually connected to the lamp driving circuit 131.

In addition, since the data NDH indicating the normal operation voltage NVH and to be referenced by the processor 133 is rewritten according to the specification of the high beam lamp 12 selected to be driven, the second voltage detecting circuit 142 can be shared by a plurality of high beam lamps 12 having different specifications. Since the second voltage detecting circuit 142 has only to have at least a function of detecting the second voltage V2, the configuration can be simplified even though both the short-circuit failure and the open failure of the high beam lamp 12 can be determined.

Therefore, it is possible to enhance the versatility of the lamp failure detecting device 15 for detecting the failure of the low beam lamp 11 and the high beam lamp 12 installed in the vehicle and connected in series.

The processor 133 capable of performing the above-described processing may be provided as a general-purpose microprocessor operating in cooperation with a general-purpose memory, or may be provided as part of a dedicated integrated circuit device, Examples of the general-purpose microprocessor include a CPU, an MPU, and a GPU. Examples of the general-purpose memory include a RAM and a ROM, A rewritable general-purpose memory may serve the function of the storage 134. Examples of the dedicated integrated circuit devices include a microcontroller, an ASIC, an FPGA, and the like. The processor 133 and the storage 134 may be provided as separate devices or may be packaged in a single device.

As illustrated in dashed lines in FIG. 2, the lamp control device 13 may include a switch 135. The switch 135 may be implemented as a semiconductor switch, such as a field effect transistor. When the switch 132 is opened by the control signal SC and the switch 135 is closed, the current supplied from the lamp driving circuit 131 bypasses the low beam lamp 11 and flows to the high beam lamp 12. Therefore, only the high beam lamp 12 can be turned on.

As illustrated in FIG. 3, the order in which the low beam lamp 11 and the high beam lamp 12 are connected in series may be exchanged. In this case, the low beam lamp 11 is an example of the first lamp from the grounding side. The high beam lamp 12 is an example of an m-th (m=2) lamp from the grounding side.

In the above embodiment, two lamps are connected in series to the lamp driving circuit 131. However, the number of lamps connected in series to the lamp driving circuit may be three or more regardless of the type.

FIG. 4 schematically illustrates a configuration of a lamp assembly 2 according to such another embodiment. The lamp assembly 2 is adapted to be installed in a vehicle. The lamp assembly 2 may be accommodated in the lamp chamber 103 of the lighting device 100 illustrated in FIG. 1.

The lamp assembly 2 comprises n lamps. The “n” is an integer of 3 or more. Then lamps include a first lamp 21, an (n−1)th lamp 2 n−1, and an n-th lamp 2 n. The first lamp 21 is connected to the grounding side of the (n−1)th lamp 2 n−1. The (n−1)th lamp 2 n−1 is connected to the grounding side of the n-th lamp 2 n. The first lamp 21 is an example of the first lamp from the grounding side.

Each of the n lamps includes at least one light source that emits light to the outside of the vehicle through the translucent cover 102 illustrated in FIG. 1, The light source may be a semiconductor light emitting element such as a light emitting diode (LED) or a laser diode (LD), or may be a lamp light source such as a halogen lamp or an HID lamp. When at least one of the n lamps comprises a plurality of light sources, the plurality of light sources are electrically connected in series.

The lamp assembly 2 includes a lamp control device 23. The n lamps are electrically connected to the lamp control device 23. The lamp control device 23 is a device configured to control the turning-on/off operation of each of the n lamps. The lamp control device 23 can be accommodated in the lamp chamber 103 of the lighting device 100 illustrated in FIG. 1.

The lamp control device 23 includes a lamp driving circuit 231. The lamp driving circuit 231 is a circuit configured to supply current for lighting n lamps. The lamp driving circuit 231 may be implemented by, for example, a step-down constant-current switching regulator (DC/DC converter).

The lamp assembly 2 includes a processor 233 and a first voltage detecting circuit 241. The first voltage detector 241 is configured to detect a first voltage V1 (=V21+ . . . +V2 n−1+V2 n), which is the sum of the voltages applied to each of the first lamp 21 to the n-th lamp 2 n. The first voltage signal SV1 corresponding to the first voltage V1 is inputted to the processor 233. The n-th lamp 2 n is an example of an m-th (m=n) lamp from the grounding side.

The first voltage detecting circuit 241 can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 4. Resistance values of respective resistive elements constituting the voltage dividing circuit can be appropriately determined based on a rated voltage applied to each of the first lamp 21 to the n-th lamp 2 n and the voltage of the first voltage signal SV1 that can be inputted to the processor 233. Depending on the specification of the processor 233, the first voltage detecting circuit 241 may include an A/D conversion circuit.

The lamp assembly 2 includes a second voltage detecting circuit 242. The second voltage detector 242 is configured to detect a second voltage V2 (=V21+ . . . +V2 n−1), which is the sum of the voltages applied to each of the first lamp 21 to the (n−1)th lamps 2 n−1. The second voltage signal SV2 corresponding to the second voltage is inputted to the processor 233. The (n−1)th lamp 2 n−1 is an example of the (m−1)th (m=n) lamp from the grounding side.

The second voltage detecting circuit 242 can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 4. Resistance values of respective resistive elements constituting the voltage dividing circuit can be appropriately determined based on a rated voltage applied to each of the first lamp 21 to the (n−1)th lamp 2 n−1 and the voltage of the second voltage signal SV2 that can be inputted to the processor 233. Depending on the specification of the processor 233, the second voltage detecting circuit 242 may include an A/D conversion circuit.

The lamp assembly 2 includes a storage 234. The storage 234 can be implemented by an appropriate rewritable semiconductor memory. The storage 234 stores data NDn indicating the normal operation voltage NVn that is to be applied when the n-th lamp 2 n is operating normally, and data NDn−1 indicating the normal operation voltage NVn−1 that is to be applied when the (n−1)th lamp 2 n−1 is operating normally. The data NDn and the data NDn−1 are rewritable. The normal operation voltage NVn may be defined as a voltage range having an upper limit value and a lower limit value. The normal operation voltage NVn−1 may be defined as a voltage range having an upper limit value and a lower limit value.

The processor 233 is configured to detect a failure of the n-th lamp 2 n based on the first voltage signal SV1 and the second voltage signal SV2.

First, the processor 233 obtains a difference VD2 between the first voltage V1 and the second voltage V2 based on the first voltage signal SV1 and the second voltage signal SV2. The difference VD2 corresponds to the voltage V2 n applied to the n-th lamp 2 n.

Subsequently, the processor 233 compares the difference value VD2 with the normal operation voltage NVn indicated by the data NDn stored in the storage 234. If the difference VD2, i.e., the voltage V2 n, is equal to the normal operation voltage NVn, the processor 233 determines that the n-th lamp 2 n is operating normally. The normal operation voltage NVn is an example of the threshold value.

If the difference value VD2 (i.e., the voltage V2 n) is more than the normal operation voltage NVn, the processor 233 determines that an open failure has occurred in the n-th lamp 2 n. When the difference value VD2 (i.e., the voltage V2 n) is less than the normal operation voltage NVn, the processor 233 determines that a short-circuit failure has occurred in the n-th lamp 2 n. An extent of which the difference value VD2 is more than the normal operation voltage NVn to determine whether the open failure has occurred can be appropriately determined. An extent of which the difference value VD2 is less than the normal operation voltage NVn to determine whether the short-circuit failure has occurred can be appropriately determined.

When any of the failures is detected in the n-th lamp 2 n, the processor 233 outputs the detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify the occupant of the vehicle that a failure has occurred in the n-th lamp 2 n, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

The lamp assembly 2 includes an n-th voltage detecting circuit 24 n. The n-th voltage detecting circuit 24 n is configured to detect an n-th voltage Vn corresponding to the voltage V21 applied to the first lamp 21. The n-th voltage signal SVn corresponding to the n-th voltage Vn is inputted to the processor 233.

The n-th voltage detecting circuit 24 n can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 4. Resistance values of respective resistive elements constituting the voltage dividing circuit may be appropriately determined based on a rated voltage applied to the first lamp 21 and the voltage of the n-th voltage signal SVn that can be inputted to the processor 233. Depending on the specification of the processor 233, the n-th voltage detecting circuit 24 n may include an A/D conversion circuit.

When n=3, the processor 233 detects a failure of the (n−1)th lamp 2 n−1 based on the second voltage signal SV2 and the n-th voltage signal SVn.

First, the processor 233 obtains the difference value VDn between the second voltage V2 and the n-th voltage Vn based on the second voltage signal SV2 and the n-th voltage signal SVn. The difference value VDn corresponds to the voltage V2 n−1 applied to the (n−1)th lamp 2 n−1.

Subsequently, the processor 233 compares the difference value VDn with the normal operation voltage NVn−1 indicated by the data NDn−1 stored in the storage 234. If the difference value VDn (i.e., the voltage Vn−1) is equal to the normal operation voltage NVn−1, the processor 233 determines that the (n−1)th lamp 2 n−1 is operating normally. The difference value VDn is an example of the threshold value.

If the difference value VDn (i.e., the voltage V2 n−1) is more than the normal operation voltage NVn−1, the processor 233 determines that an open failure has occurred in the (n−1)th lamp 2 n−1. If the difference value VDn (i.e., the voltage Vn−1) is less than the normal operation voltage NVn−1, the processor 233 determines that a short-circuit failure has occurred in the (n−1)th lamp 2 n−1. An extent of which the difference value VDn is more than the normal operation voltage NVn−1 to determine whether the open failure has occurred can be appropriately determined. An extent of which the difference value VDn is less than the normal operation voltage NVn−1 to determine whether the short-circuit failure has occurred can be appropriately determined.

When any one of the failures is detected in the (n−1)th lamp 2 n−1, the processor 233 outputs the detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify the occupant of the vehicle that a failure has occurred in the (n−1)th lamp 2 n−1, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

The storage 234 stores data ND1 indicating a normal operation voltage NV1 that is to be applied when the first lamp 21 is operating normally. The data ND1 is rewritable. The normal operation voltage NV1 may be defined as a voltage range having an upper limit value and a lower limit value.

The processor 233 compares the n-th voltage Vn corresponding to the n-th voltage signal SVn with the normal operation voltage NV1 indicated by the data ND1 stored in the storage 234. If the n-th voltage Vn (i.e., the voltage V21) is equal to the normal operation voltage NV1, the processor 233 determines that the first lamp 21 is operating normally.

If the n-th voltage Vn (i.e., the voltage V21) is more than the normal operation voltage NV1, the processor 233 determines that an open failure has occurred in the first lamp 21. If the n-th voltage Vn (i.e., the voltage V21) is less than the normal operation voltage NV1, the processor 233 determines that a short-circuit failure has occurred in the first lamp 21. An extent of which the n-th voltage Vn is more than the normal operation voltage NV1 to determine whether the open failure has occurred can be determined as appropriate. An extent of which the n-th voltage Vn is less than the normal operation voltage NV1 to determine whether the short-circuit failure has occurred can be determined as appropriate.

If any failure is detected in the first lamp 21, the processor 233 outputs a detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify the occupant of the vehicle that a failure has occurred in the first lamp 21, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

That is, the processor 233 detects, for arbitrary n, the failure of the (n-m+2)th lamp from the grounding side based on the (m−1)th voltage signal SVm−1 outputted from the (m−1)th voltage detecting circuit and the m-th voltage signal SVm outputted from the m-th voltage detecting circuit (m is an arbitrary integer of no less than 2 and no more than n). The (m−1)th voltage detecting circuit is an example of the first voltage detecting circuit. The sum of the voltages applied to each of the first lamp to the (n−m+2)th lamp from the grounding side is an example of the first voltage. The m-th voltage detecting circuit is an example of the second voltage detecting circuit. The sum of the voltages applied to each of the first lamp to the (n−m+1)th lamp from the grounding side is an example of the second voltage. The difference value between the first voltage and the second voltage is an example of the threshold value.

The first voltage detecting circuit 241, the second voltage detecting circuit 242, the n-th voltage detecting circuit 24 n, and the processor 233 constitute a lamp failure detecting device 25.

As described above, the data ND1 to NDn stored in the storage 234 are rewritable. Therefore, the lamp failure detecting device 25 can be initialized by the following procedure.

First, n lamps constituting the lamp assembly 2 are selected. The selected n lamps are electrically connected in series to the lamp control device 23.

The normal operation voltage applied to each of the n lamps when it is operating normally differs from individual to individual. Thus, for the selected n lamps, the normal operation voltages NV1 to NVn are obtained through measurements.

Subsequently, the data ND1 to NDn corresponding to the acquired normal operation voltages NV1 to NVn of the n lamps are stored in the storage 234. In other words, the processor 233 is placed in a condition that is able to reference the normal operation voltages NV1 to NVn. When any data ND1 to NDn have already stored in the storage 234, they are rewritten with the data ND1 to NDn corresponding to the newly acquired normal operation voltages NV1 to NVn.

According to the above-described configuration, the voltage Vm itself applied to the m-th lamp 2 m (m is an integer of no less than 2 and no more than n) among the n lamps (n is an integer of no less than 2) each including at least one light source and connected in series is not detected by a specific voltage detecting circuit. Instead, the difference between the first voltage, which is the sum of the voltages applied to each of the first lamp 21 to the m-th lamp, and the second voltage, which is the sum of the voltages applied to each of the first lamp 21 to the m-th lamp 2 m−1, is treated as the voltage Vm applied to the m-th lamp 2 m and is subjected to comparison with the normal operation voltage NVm that is to be referenced by the processor 233.

On the other hand, the data NDm indicating the normal operation voltages NVm and to be referenced by the processor 233 is rewritten in accordance with the specifications of the m-th lamp 2 m selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage NVm of the m-th lamp 2 m is eliminated, and both the short-circuit failure and the open failure of the m-th lamp 2 m are accurately determined by the comparison between the above-described difference value and the normal operation voltage NVm of the m-th lamp 2 m that is actually connected to the lamp driving circuit 231.

In addition, since the data ND1 to NDn indicating the normal operation voltages NV1 to NVn and to be referenced by the processor 233 are rewritten in accordance with the specifications of the n lamps selected to be driven, the voltage detecting circuit can be shared by the n lamps having different specifications. Since the voltage detecting circuit has only to have at least the function of detecting the first voltage and the second voltage described above, the configuration can be simplified even though both the short-circuit failure and the open failure of each lamp can be determined.

Therefore, it is possible to enhance the versatility of the lamp failure detecting device 25 for detecting the failure of a plurality of lamps installed in the vehicle and connected in series.

The lamp assembly 2 may include a switch 232. The switch 232 may be implemented as a semiconductor switch, such as a field effect transistor. By controlling the operation of the switch 232, the processor 233 may determine whether or not the current from the lamp driving circuit 231 is supplied to at least one of the first lamp 21 to the (n−1)th lamp 2 n−1. The processor 233 outputs a control signal SC for switching the open/closed state of the switch 232. The control signal SC may be, for example, a signal for changing a control terminal voltage of a corresponding semiconductor switch.

In the embodiment illustrated in FIG. 4, when the switch 232 is closed by the control signal SC, a path is so formed that current is supplied from the lamp driving circuit 23 to the n-th lamp 2 n only while bypassing the first lamp 21 to the (n−1) lamp 2 n−1. As a result, only the n-th lamp 2 n is turned on.

When the switch 232 is opened by the control signal SC, a path is so formed that current is supplied from the lamp driving circuit 231 to all the lamps. As a result, all lamps are turned on.

According to such a configuration, the on/off state of at least one of the plurality of lamps connected in series to the lamp driving circuit 231 can be individually controlled. The number and arrangement of the switches 232 in the lamp control device 23 may be appropriately determined depending on the number of lamps and the positions in the series connection which require individual control of the on/off state.

The processor 233 capable of performing the above-described processing may be provided as a general-purpose microprocessor operating in cooperation with a general-purpose memory, or may be provided as part of a dedicated integrated circuit device. Examples of the general-purpose microprocessor include a CPU, an MPU, and a GPU. Examples of the general-purpose memory include a RAM and a ROM. A rewritable general-purpose memory may serve the function of the storage 234. Examples of the dedicated integrated circuit devices include a microcontroller, an ASIC, an FPGA, and the like. The processor 233 and the storage 234 may be provided as separate devices or may be packaged in a single device.

FIG. 5 schematically illustrates a configuration of a light source assembly 3 according to one embodiment. The light source assembly 3 is adapted to be installed in a vehicle. The light source assembly 3 may be accommodated in a lamp chamber 103 of the lighting device 100 illustrated in FIG. 1.

The light source assembly 3 comprises a first light source 31 and a second light source 32. The first light source 31 and the second light source 32 are electrically connected in series. Each of the first light source 31 and the second light source 32 may be a semiconductor light emitting device such as a light emitting diode (LED) or a laser diode (LD), or may be a lamp light source such as a halogen lamp or an HID lamp. Each of the first light source 31 and the second light source 32 may be a part of a common lamp 30. The translucent cover 102 illustrated in FIG. 1 allows the passage of light emitted from each of the first light source 31 and the second light source 32.

The second light source 32 is an example of the first light source from the grounding side. The first light source 31 is an example of the m-th (m=2) light source from the grounding side.

The light source assembly 3 includes a light source control device 33, The first light source 31 and the second light source 32 are electrically connected to the light source control device 33. The light source control device 33 is a device configured to control the turning-on/off operation of each of the first light source 31 and the second light source 32. The light source control device 33 may be accommodated in the lamp chamber 103 of the lighting device 100 illustrated in FIG. 1.

The light source control device 33 includes a light source driving circuit 331. The light source driving circuit 331 is a circuit configured to supply current for lighting the first light source 31 and the second light source 32. The light source driving circuit 331 may be implemented by, for example, a step-down constant-current switching regulator (DC/DC converter).

The light source assembly 3 includes a processor 333 and a first voltage detecting circuit 341. The first voltage detecting circuit 341 is configured to detect the first voltage V1 which is the sum of the voltage V31 applied to the first light source 31 and the voltage V32 applied to the second light source 32. The first voltage signal SV1 corresponding to the first voltage V1 is inputted to the processor 333.

The first voltage detecting circuit 341 can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 5. Resistance values of respective resistive elements constituting the voltage dividing circuit can be appropriately determined based on a rated voltage applied to the first light source 31 and the second light source 32 as well as the voltage of the first voltage signal SV1 that can be inputted to the processor 333. Depending on the specification of the processor 333, the first voltage detecting circuit 341 may include an A/D conversion circuit.

The light source assembly 3 includes a second voltage detecting circuit 342. The second voltage detecting circuit 342 is configured to detect a second voltage V2 corresponding to the voltage V32 applied to the second light source 32. The second voltage signal SV2 corresponding to the second voltage V2 is inputted to the processor 333.

The second voltage detecting circuit 342 can be implemented by, for example, a simple voltage dividing circuit as illustrated in FIG. 5. Resistance values of respective resistive elements constituting the voltage dividing circuit can be appropriately determined based on a rated voltage applied to the second light source 32 and the voltage of the second voltage signal SV2 that can be inputted to the processor 333. Depending on the specification of the processor 333, the second voltage detecting circuit 342 may include an A/D conversion circuit.

The light source assembly 3 includes a storage 334. The storage 334 can be implemented by an appropriate rewritable semiconductor memory. The storage 334 stores data ND1 indicating the normal operation voltage NV1 that is to be applied when the first light source 31 is operating normally, and data ND2 indicating the normal operation voltage NV2 that is to be applied when the second light source 32 is operating normally. The data ND1 and the data ND2 are rewritable. The normal operation voltage NV1 may be defined as a voltage range having an upper limit value and a lower limit value. The normal operation voltage NV2 may be defined as a voltage range having an upper limit value and a lower limit value.

The processor 333 is configured to detect a failure of each of the first light source 31 and the second light source 32 based on the first voltage signal SV1 and the second voltage signal SV2.

First, the processor 333 obtains a difference VD between the first voltage V1 and the second voltage V2 based on the first voltage signal SV1 and the second voltage signal SV2. The difference value VD corresponds to the voltage V31 applied to the first light source 31.

Subsequently, the processor 333 compares the difference value VD with the normal operation voltage NV1 indicated by the data ND1 stored in the storage 334. If the difference value VD (i.e., the voltage V31) is equal to the normal operation voltage NV1, the processor 333 determines that the first light source 31 is operating normally. The normal operation voltage NV1 is an example of the threshold value.

If the difference value VD (i.e., the voltage V31) is more than the normal operation voltage NV1, the processor 333 determines that an open failure has occurred in the first light source 31. If the difference value VD (i.e., the voltage V31) is less than the normal operation voltage NV1, the processor 333 determines that a short-circuit failure has occurred in the first light source 31. An extent of which the difference value VD is more than the normal operation voltage NV1 to determine whether the open failure has occurred can be determined as appropriate. An extent of which the difference value VD is less than the normal operation voltage NV1 to determine whether the short-circuit failure has occurred can be determined as appropriate.

If any failure is detected in the first light source 31, the processor 333 outputs a detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify the occupant of the vehicle that a failure has occurred in the first light source 31, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

Similarly, the processor 333 compares the second voltage V2 corresponding to the second voltage signal SV2 with the normal operation voltage NV2 indicated by the data ND2 stored in the storage 334. If the second voltage V2 (i.e., the voltage V32) is equal to the normal operation voltage NV2, the processor 333 determines that the second light source 32 is operating normally.

If the second voltage V2 (i.e., the voltage V32) is more than the normal operation voltage NV2, the processor 333 determines that an open failure has occurred in the second light source 32. If the second voltage V2 (i.e., the voltage V32) is less than the normal operation voltage NV2, the processor 333 determines that a short-circuit failure has occurred in the second light source 32. An extent of which the second voltage V2 is more than the normal operation voltage NV2 to determine whether the open failure has occurred can be determined as appropriate. An extent of which the second voltage V2 is less than the normal operation voltage NV2 to determine whether the short-circuit failure has occurred can be determined as appropriate.

If any failure is detected in the second light source 32, the processor 333 outputs a detecting signal SD. The detecting signal SD may be transmitted to other control devices in the vehicle. For example, the other control device may notify the occupant of the vehicle that a failure has occurred in the second light source 32, based on the detecting signal SD. Notifications may be made through at least one of a visual manner, an audible manner and a haptic manner.

The first voltage detecting circuit 341, the second voltage detecting circuit 342, and the processor 333 constitute a light source failure detecting device 35.

As described above, the data ND1 and the data ND2 stored in the storage 334 are rewritable. Therefore, the light source failure detecting device 35 can be initialized by the following procedure.

First, a first light source 31 and a second light source 32 constituting the light source assembly 3 are selected. The selected first light source 31 and second light source 32 are electrically connected in series to the light source control device 33.

The normal operation voltage NV1 applied to the first light source 31 when it is operating normally (e.g., the forward voltage in the case of the light emitting diode) differs from individual to individual. Thus, the normal operation voltage NV1 of the selected first light source 31 is obtained through measurement.

Similarly, the normal operation voltage NV2 applied to the second light source 32 when it is operating normally differs from individual to individual. Thus, the normal operation voltage NV2 of the selected second light source 32 is obtained through measurement.

Subsequently, the data ND1 corresponding to the acquired normal operation voltage NV1 of the first light source 31 is stored in the storage 334. In other words, the processor 333 is placed in a condition that is able to reference the normal operation voltage NV1. When any data ND1 has already stored in the storage 334, it is rewritten with the data ND1 corresponding to the newly acquired normal operation voltage NV1.

Similarly, the data ND2 corresponding to the acquired normal operation voltage NV2 of the second light source 32 is stored in the storage 334. In other words, the processor 333 is placed in a condition that is able to reference the normal operation voltage NV2. When any data ND2 has already stored in the storage 334, it is rewritten with the data ND2 corresponding to the newly acquired normal operation voltage NV2.

According to the above configuration, the voltage V31 itself applied to the first light source 31 is not detected by a specific voltage detecting circuit. Instead, the difference value VD between the first voltage V1, which is the sum of the voltages applied to the first light source 31 and the second light source 32, and the second voltage V2, which corresponds to the voltage V32 applied to the second light source 32, is treated as the voltage V31 applied to the first light source 31 and is subjected to comparison with the normal operation voltage that is to be referenced by the processor 333.

On the other hand, the data ND1 indicating the normal operation voltage NV1 and to be referenced by the processor 333 is rewritten in accordance with the specification of the first light source 31 selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage NV1 of the first light source 31 is eliminated, and both the short-circuit failure and the open failure of the first light source 31 are accurately determined by the comparison between the difference value VD and the normal operation voltage NV1 of the first light source 31 that is actually connected to the light source driving circuit 331.

Further, since the data ND1 indicating the normal operation voltage NV1 and to be referenced by the processor 333 is rewritten according to the specification of the first light source 31 selected to be driven, the first voltage detecting circuit 341 and the second voltage detecting circuit 342 can be shared by the plurality of first light sources 31 having different specifications. Since each of the first voltage detecting circuit 341 and the second voltage detecting circuit 342 has only to have at least the function of detecting the first voltage V1 and the second voltage V2 described above, the configuration can be simplified even though both the short-circuit failure and the open failure of the first light source 31 can be determined.

Similarly, the data ND2 indicating the normal operation voltage NV2 and to be referenced by the processor 333 is rewritten according to the specification of the second light source 32 selected to be driven. Therefore, the influence of the inter-individual variation in the normal operation voltage NV2 of the second light source 32 is eliminated, and both the short-circuit failure and the open failure of the second light source 32 are accurately determined by the comparison between the second voltage V2 and the normal operation voltage NV2 of the second light source 32 that is actually connected to the light source driving circuit 331.

In addition, since the data ND2 indicating the normal operation voltage NV2 and to be referenced by the processor 333 is rewritten according to the specification of the second light source 32 selected to be driven, the second voltage detecting circuit 342 can be shared by the plurality of second light sources 32 having different specifications. Since the second voltage detecting circuit 342 has only to have at least a function of detecting the second voltage V2, the configuration can be simplified even though both the short-circuit failure and the open failure of the second light source 32 can be determined.

Therefore, it is possible to improve the versatility of the light source failure detecting device 35 for detecting the failure of the first light source 31 and the second light source 32 installed in the vehicle and connected in series.

In the above embodiment, two light sources are connected in series to the light source driving circuit 331. However, the plurality of light sources connected in series to the light source driving circuit may be three or more regardless of the type. In this case, the failure of each light source can be detected by the same configuration and method as those of the lamp failure detecting device 25 described with reference to FIG. 4.

The processor 333 capable of performing the above-described processing may be provided as a general-purpose microprocessor operating in cooperation with a general-purpose memory, or may be provided as part of a dedicated integrated circuit device, Examples of the general-purpose microprocessor include a CPU, an MPU, and a GPU. Examples of the general-purpose memory include a RAM and a ROM. A rewritable general-purpose memory may serve the function of the storage 334. Examples of the dedicated integrated circuit devices include a microcontroller, an ASIC, an FPGA, and the like. The processor 333 and the storage 334 may be provided as separate devices or may be packaged in a single device.

The above embodiments are merely illustrative to facilitate understanding of the presently disclosed subject matter. The configuration according to each of the above embodiments can be appropriately modified or improved without departing from the gist of the presently disclosed subject matter. 

1. A lamp assembly adapted to be installed in a vehicle, comprising: n lamps (n is an integer no less than 2) connected in series, each of which includes at least one light source; a lamp driving circuit configured to supply current to each of the n lamps; a first voltage detecting circuit configured to detect a first voltage that is a sum of voltages applied to each of a first lamp to an m-th lamp (m is an integer no less than 2 and no more than n) from a grounding side; a second voltage detecting circuit configured to detect a second voltage that is a sum of voltages applied to each of the first lamp to an (m−1)th lamp from the grounding side; and a processor configured to obtain a difference between the first voltage and the second voltage, and to detect a failure in the m-th lamp based on comparison between the difference and a rewritable threshold value.
 2. The lamp assembly according to claim 1, comprising: a switch configured to determine whether or not the current is supplied to at least one of the first lamp to an (n−1)th lamp from the grounding side.
 3. The lamp assembly according to claim 1, wherein the n-th lamp from the grounding side is a low beam lamp; and wherein at least one lamp except the n-th lamp is a high beam lamp.
 4. A lamp failure detecting device adapted to be installed in a vehicle, comprising: a first voltage detecting circuit configured to detect a first voltage that is a sum of voltages applied to, among n lamps (n is an integer no less than 2) connected in series each of which includes at least one light source, each of a first lamp to an m-th lamp (m is an integer no less than 2 and no more than n) from a grounding side; a second voltage detecting circuit configured to detect a second voltage that is a sum of voltages applied to each of the first lamp to an (m−1)th lamp from the grounding side; and a processor configured to obtain a difference between the first voltage and the second voltage, and to detect a failure in the m-th lamp based on comparison between the difference and a rewritable threshold value.
 5. A method of setting the lamp failure detecting device according to claim 4, comprising: selecting the m-th lamp to be connected to a lamp driving circuit from which current is supplied; obtaining a normal operation voltage of the m-th lamp that is to be applied when the m-th lamp is operating normally; and enabling the processor to reference the normal operation voltage as the threshold value.
 6. A light source failure detecting device adapted to be installed in a vehicle, comprising: a first voltage detecting circuit configured to detect a first voltage that is a sum of voltages applied to, among n light sources (n is an integer no less than 2) connected in series, each of a first light source to an m-th light source (m is an integer no less than 2 and no more than n) from a grounding side; a second voltage detecting circuit configured to detect a second voltage that is a sum of voltages applied to each of the first light source to an (m−1)th light source from the grounding side; and a processor configured to obtain a difference between the first voltage and the second voltage, and to detect a failure in the m-th light source based on comparison between the difference and a rewritable threshold value.
 7. A method of setting the light source failure detecting device according to claim 6, comprising: selecting the m-th light source to be connected to a light source from which current is supplied; obtaining a normal operation voltage of the m-th light source that is to be applied when the m-th light source is operating normally; and enabling the processor to reference the normal operation voltage as the threshold value. 